Social image concerns promote cooperation more than altruistic punishment

Human cooperation is enigmatic, as organisms are expected, by evolutionary and economic theory, to act principally in their own interests. However, cooperation requires individuals to sacrifice resources for each other’s benefit. We conducted a series of novel experiments in a foraging society where social institutions make the study of social image and punishment particularly salient. Participants played simple cooperation games where they could punish non-cooperators, promote a positive social image or do so in combination with one another. We show that although all these mechanisms raise cooperation above baseline levels, only when social image alone is at stake do average economic gains rise significantly above baseline. Punishment, either alone or combined with social image building, yields lower gains. Individuals’ desire to establish a positive social image thus emerges as a more decisive factor than punishment in promoting human cooperation.We acknowledge financial support from the German Federal Ministry of Education and Research through the project ‘BIOACID (03F0655H)’, the Spanish Ministerio de Ciencia e Innovación (grant ECO 2011-23634), the Spanish Ministerio de Economía y Competitividad (project ECO 2015-68469-R), the Universidad Jaume I (P1.1B2015-48) and the Kiel Institute for the World Economy. We especially thank our local assistants Eliuda Maravut, Horai Magum, Philippe Hus, Nigel Henry, Saeleah Gordon and Siko Gordon. We thank Vincent Richrath and Irene Jimenez Arribas for research assistance, and Heike Hennig-Schmidt for discussion

Homo Æqualis: A Cross-Society Experimental Analysis of Three Bargaining Games

Data from three bargaining games-the Dictator Game, the Ultimatum Game, and the Third-Party Punishment Game-played in 15 societies are presented. The societies range from US undergraduates to Amazonian, Arctic, and African hunter-gatherers. Behaviour within the games varies markedly across societies. The paper investigates whether this behavioural diversity can be explained solely by variations in inequality aversion. Combining a single parameter utility function with the notion of subgame perfection generates a number of testable predictions. While most of these are supported, there are some telling divergences between theory and data: uncertainty and preferences relating to acts of vengeance may have influenced play in the Ultimatum and Third-Party Punishment Games; and a few subjects used the games as an opportunity to engage in costly signalling.

“Economic man” in cross-cultural perspective: Behavioral experiments in 15 small-scale societies

Researchers from across the social sciences have found consistent deviations from the predictions of the canonical model of self-interest in hundreds of experiments from around the world. This research, however, cannot determine whether the uniformity results from universal patterns of human behavior or from the limited cultural variation available among the university students used in virtually all prior experimental work. To address this, we undertook a cross-cultural study of behavior in ultimatum, public goods, and dictator games in a range of small-scale societies exhibiting a wide variety of economic and cultural conditions. We found, first, that the canonical model – based on self-interest – fails in all of the societies studied. Second, our data reveal substantially more behavioral variability across social groups than has been found in previous research. Third, group-level differences in economic organization and the structure of social interactions explain a substantial portion of the behavioral variation across societies: the higher the degree of market integration and the higher the payoffs to cooperation in everyday life, the greater the level of prosociality expressed in experimental games. Fourth, the available individual-level economic and demographic variables do not consistently explain game behavior, either within or across groups. Fifth, in many cases experimental play appears to reflect the common interactional patterns of everyday life

Markets, Religion, Community Size, and the Evolution of Fairness and Punishment

Large-scale societies in which strangers regularly engage in mutually beneficial transactions are puzzling. The evolutionary mechanisms associated with kinship and reciprocity, which underpin much of primate sociality, do not readily extend to large unrelated groups. Theory suggests that the evolution of such societies may have required norms and institutions that sustain fairness in ephemeral exchanges. If that is true, then engagement in larger-scale institutions, such as markets and world religions, should be associated with greater fairness, and larger communities should punish unfairness more. Using three behavioral experiments administered across 15 diverse populations, we show that market integration (measured as the percentage of purchased calories) positively covaries with fairness while community size positively covaries with punishment. Participation in a world religion is associated with fairness, although not across all measures. These results suggest that modern prosociality is not solely the product of an innate psychology, but also reflects norms and institutions that have emerged over the course of human history

Costly Punishment Across Human Societies

Recent behavioral experiments aimed at understanding the evolutionary foundations of human cooperation have suggested that a willingness to engage in costly punishment, even in one-shot situations, may be part of human psychology and a key element in understanding our sociality. However, because most experiments have been confined to students in industrialized societies, generalizations of these insights to the species have necessarily been tentative. Here, experimental results from 15 diverse populations show that (i) all populations demonstrate some willingness to administer costly punishment as unequal behavior increases, (ii) the magnitude of this punishment varies substantially across populations, and (iii) costly punishment positively covaries with altruistic behavior across populations. These findings are consistent with models of the gene-culture coevolution of human altruism and further sharpen what any theory of human cooperation needs to explain

Reply to van Hoorn: Converging lines of evidence

We agree with the comments by van Hoorn (1) on our critique (2): testing causal hypotheses about human behavior is a challenge (1, 3). Making progress requires specifying alternative hypotheses and then testing these hypotheses using diverse and converging lines of evidence. We have defended the hypothesis that social norms, which culturally coevolved with the institutions of large-scale societies including markets, influence economic decision-making. This hypothesis emerged from a larger set that we developed both at the outset of our project and as we went along. Our interdisciplinary team’s initial list of hypotheses included the idea that experimental games might spark an innate reciprocity module that would yield little variation across populations

The interaction of nutrition and fertility among Au forager-horticulturalists of Papua New Guinea.

The major goals of this study were to examine the effects of repeated reproductive episodes on the nutritional status of mothers, and on the growth and development of their offspring in a small natural fertility population. The study was conducted over a 16 month period among the Au forager-horticulturalists of Papua New Guinea. Anthropometric, bioelectrical impedance, and hematological measures of nutritional status were taken on 500 Au mothers of known ages and parities. Birth weights and data on weight and recumbent length were collected for 800 Au children aged 0 to 5 years. Finally, data on breast-feeding and supplementation patterns, and duration of postpartum amenorrhea were collected for 300 mother-offspring pairs. A series of probit analyses indicates that the Au have one of the longest durations of breast-feeding (43 months), and postpartum amenorrhea (25 months) ever reported. Moreover, when a sample of over 400 mothers is stratified by percent body fat, an inverse relationship between fatness and the duration of postpartum amenorrhea is apparent. Neither differences in breast-feeding patterns, nor supplementation can completely account for this effect. Thus, this study demonstrates a significant effect of maternal nutritional status on postpartum amenorrhea independent of breast-feeding patterns. Another major finding of this research is that the adiposity of Au mothers declines throughout the period of lactation. This short-term decline in adiposity also continues over successive reproductive episodes. Thus, Au mothers exhibit a progressive depletion of their stored energy reserves over the course of their reproductive life spans. This finding corroborates the prediction of evolutionary theory that organisms engage in trade-offs between their reproductive and somatic energy budgets, and that every round of reproduction entails a reduction in the residual reproductive energy of the parent. Finally, although the birth weights of Au neonates and their growth velocity during the first 5 years of life are extremely low, no birth order-related variation in either prenatal or postnatal growth was detected. This suggests that fertility-related maternal depletion may be a coping mechanism that assists chronically-undernourished mothers in producing viable offspring.Ph.D.Health and Environmental SciencesNutritionPhysical anthropologySocial SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128781/2/9135710.pd